The present invention is directed to toners, developers, and imaging processes, including a process for forming color images, and more specifically, the present invention is directed to a process for obtaining two-color images which in an embodiment comprises charging an imaging member, creating on the member a latent image comprising areas of high, medium, and low potential, developing the low areas of potential with a positive charged colored developer composition, referred to in an embodiment as discharge area development (DAD), subsequently developing the high areas of potential with a negative charged black developer composition, referred to as charged area development (CAD), transferring the developed images to a substrate, and optionally permanently affixing the image to the substrate. The positive charged color developer composition, which in an embodiment of the present invention, is comprised of a negatively charged blue toner comprised, for example, of resin, a positive charging colored pigment as the primary pigment, such as PV Fast Blue, and a negative charging pigment, such as Neopen Blue or Sudan Blue OS as a charge enhancing additive, can be selected for the development of the low areas of potential; thereafter, the high areas of potential can be developed with a negatively charged black developer composition comprised of a positively charged black toner, comprised, for example, of a resin, carbon black and a charge enhancing additive, transferring both the color and black developed images to a substrate, and permanently affixing the images to the substrate by, for example, heat or a combination of heat and pressure. In another embodiment, the negatively charged toner can be comprised of resin particles, positively charging pigment particles, such as PV Fast blue, negatively charging pigment particles, such as Neopen Blue OS, or Sudan Blue OS, and optional known charge additives or mixtures thereof, such as distearyl dimethyl ammonium methyl sulfate, can be utilized, which additives may be present in various effective amounts, such as for example from about 0.5 to about 2 weight percent; which toner can be selected for the development of low areas of potential in, for example, xerographic imaging and printing processes; and wherein a positively charged black toner can be selected for the development of high areas of potential. One positively charged toner in an embodiment is comprised of resin particles, such as Pliotones.TM., colored pigment particles, such as PV fast Blue, 7 weight percent for example, and a known charge additive, such as distearyl dimethyl ammonium methyl sulfate, 5 weight percent for example; and one negatively charged toner can be comprised of Pliotone.TM., PV Fast Blue, 6 weight percent for example, Neopen Blue, 1 weight percent for example, and a known charge additive, such as distearyl dimethyl ammonium methyl sulfate, 0.5 weight percent for example. In one development process embodiment of the present invention, there can be selected the toners and developers as illustrated herein for the methods as illustated in U.S. Pat. No. 4,078,929, the disclosure of which is totally incorporated herein by reference.
One advantage associated with the toners and processes of the present invention is the ability to generate high quality two-color images in a single development pass, particularly as a result of the absence of interaction between the colored, excluding black, and the black developers in an embodiment of the present invention. Other advantages associated with the present invention include the provision of a triboelectrically stable colored developer comprised of a negative charging color toner which enables the generation of high quality images subsequent to development, that is images with substantially no background deposits. Another advantage associated with the present invention in embodiments thereof resides in the enablement of a positive charging pigment in a negative charging toner formulation by the use of a negative charging pigment as a charge enhancing additive. This permits in embodiments the use of a significantly broader range of color pigments for use in negative charging color toners and through use of two pigments enables a toner composition for a range of color space usually not attainable with use of a single pigment.
Processes for obtaining electrophotographic, including xerographic, and two-colored images are known. In U.S. Pat. No. 4,264,185, the disclosure of which is totally incorporated herein by reference, there is illustrated an apparatus for forming two-color images by forming a bipolar electrostatic image of a two-color original document on a photoconductive drum. A first developing unit applies a toner of a first color and polarity to the drum and a second developing unit applies a toner of a second color and polarity to the drum to form a two-color electrostatic image which is transferred and fixed to a copy sheet. A bias voltage of the first polarity is applied to the second developing unit to repel the toner of the first color and prevent degradation of the first color toner image. A bias voltage of the second polarity is applied to the first developing unit to prevent contamination of the first color toner with the second color toner.
In U.S. Pat. No. 4,308,821, the disclosure of which is totally incorporated herein by reference, there is illustrated a method and apparatus for forming two-color images which employs two magnetic brushes. The first developed image is not disturbed during development of the second image since the second magnetic brush contacts the surface of the imaging member more lightly than the first magnetic brush, and the toner scraping force of the second magnetic brush is reduced in comparison with that of the first magnetic brush by setting the magnetic flux density on a second nonmagnetic sleeve with an internally disposed magnet smaller than the magnetic flux density on a first magnetic sleeve, or by adjusting the distance between the second nonmagnetic sleeve and the surface of the imaging member. In addition, the toners selected may have different quantities of electric charge.
Further, U.S. Pat. No. 4,378,415, the disclosure of which is totally incorporated herein by reference, illustrates a method of highlight color imaging which comprises providing a layered organic photoreceptor having a red sensitive layer and a short wavelength sensitive layer, subjecting the imaging member to negative charges, followed by subjecting the imaging member to positive charges, imagewise exposing the member, and developing with a colored developer composition comprising positively charged toner components, negatively charged toner components and carrier particles. In U.S. Pat. No. 4,430,402, there is illustrated a two component type dry developer for use in dichromatic electrophotography which comprises two kinds of developers, each of which consists of a toner and a carrier. Dichromatic images are formed by developing a both positively and negatively electrified electrostatic latent image successively with toners different in polarity and color from each other, wherein one carrier becomes positively charged by friction with either of the two toners while the other carrier becomes negatively charged by friction with either of the two toners.
Additionally, U.S. Pat. No. 4,594,302, the disclosure of which is totally incorporated herein by reference, there is illustrated a developing process for two-colored electrophotography which comprises charging the surface of a photoreceptor with two photosensitive layers of different spectral sensitivities with one polarity, subsequently charging the photoreceptor with a different polarity, exposing a two-colored original to form electrostatic latent images having different polarities corresponding to the two-colored original, developing one latent image with a first color toner of one polarity, exposing the photoreceptor to eliminate electric charges with the same polarity as the first color toner which are induced on the surface of the photoreceptor in the vicinity of the latent image with a second color toner charged with a polarity different from that of the first color toner.
In addition, U.S. Pat. No. 4,500,616, the disclosure of which is totally incorporated herein by reference, discloses a method of developing electrostatic latent images by selectively extracting colored grains of one polarity from a mixture containing colored grains having opposite polarity to each other in the presence of an alternating field, followed by development of the electrostatic image by the selectively extracted colored grains. Further, U.S. Pat. No. 4,524,117, the disclosure of which is totally incorporated herein by reference, discloses an electrophotographic method for forming two-colored images which comprises uniformly charging the surface of a photoreceptor having a conductive surface and a photoconductive layer sensitive to a first color formed on the conductive substance, followed by exposing a two-colored original to form on the photoconductive layer a latent image corresponding to a second color region in the original with the same polarity as the electric charges on the surface of the photoconductive layer. The photoreceptor surface is then subjected to a reversal development treatment by the use of a photoconductive color toner charged with the same polarity as the electric charges constituting the latent image to develop the noncharged region with the photoconductive toner. The latent image is then subjected to normal development treatment with an insulative toner having a color different from the color of the photoconductive toner. Subsequently, the color toners on the photoconductive layer are charged with a different polarity from the charging polarity and, simultaneously, the original is exposed through a filter shielding against the first color thereby forming a two-colored image.
Furthermore, in U.S. Pat. No. 4,525,447, the disclosure of which is totally incorporated herein by reference, there is illustrated an image forming method which comprises forming on a photosensitive member an electrostatic latent image having at least three different levels of potentials, or comprising first and second latent images and developing the first and second latent images with a three component developer. The developer comprises a magnetic carrier, a first toner chargeable to one polarity by contact with the magnetic carrier, and a second toner chargeable to a polarity opposite to that of the first toner by contact with the first toner, but substantially not chargeable by contact with the magnetic carrier. Also, U.S. Pat. No. 4,539,281 discloses a method of forming dichromatic copy images by forming an electrostatic latent image having a first image portion and a second image portion. The first image portion is developed by a first magnetic brush with a magnetic toner of a first color that is chargeable to a specific polarity, and the second image portion is developed by a second magnetic brush with a mixture of a magnetic carrier substantially not chargeable with the magnetic toner and a nonmagnetic toner of a second color chargeable to a polarity opposite to that of the magnetic toner by contact with the magnetic carrier.
Additionally, U.S. Pat. No. 4,562,129, the disclosure of which is totally incorporated herein by reference, illustrates a method of forming dichromatic copy images with a developer composed of a high-resistivity magnetic carrier and a nonmagnetic insulating toner, which are triboelectrically chargeable. An electrostatic latent image having at least three different levels of potential is formed and the toner and carrier are adhered, respectively, onto the first and second image portions. In addition, U.S. Pat. No. 4,640,883, the disclosure of which is totally incorporated herein by reference, illustrates a method of forming composite or dichromatic images which comprises forming on an imaging member electrostatic latent images having at least three different potential levels, the first and second latent images being represented, respectively, by a first potential and a second potential relative to a common background potential. The first and second images are developed by a first magnetic brush using two kinds of toners, at least one of which is magnetic, and both of which are chargeable to polarities opposite to each other with application to a developing electrode of a bias voltage capable of depositing the magnetic toner on the background potential area to deposit selectively the two toners on the first and second latent images and to deposit the magnetic toner on the background potential area, while collecting the deposited magnetic toner at least from the background potential area by second magnetic brush developing means.
Also mentioned are the following U.S. Pat. Nos. 4,845,004 directed to hydrophobic silicon type micropowders comprising silicon type microparticles which have been treated with secondary tertiary amine functional silanes, and when the micropowders combine with the positively charging resin powder, such as a toner, the fluidity of the resin powder is substantially increased, see for example the Abstract of the Disclosure, column 1, beginning at line 60, and continuing on to column 4 and the working Examples; 4,758,491 directed to dry toner and developer compositions with good charge stability and minimization of toner image transfer defects, which composition comprises a major component of a normally solid fixable binder resin which is free of siloxane segments and is a minor component in a normally solid multiphase thermoplastic condensate polymer which contains a polyorgano siloxane block or graft segment, note specifically the use of a charge control agent in column 2, beginning at line 50, examples of charge control agents being detailed, for example, in column 4, beginning at line 23, including ammonium or phosphonium salts, and the like; 4,845,003 directed to a toner for developing electrostatic latent images characterized in that the toner comprises an aluminum compound of a hydroxy carboxylic acid which may be substituted with alkyl and/or arylalkyl, see for example column 2, beginning at line 29, and continuing on to column 5; and 4,855,208 directed to a toner for developing electrostatic latent images, which toner comprises an aluminum compound of an aromatic amino carboxylic acid as represented by the formula illustrated in the Abstract of the Disclosure, and also see column 2, beginning at line 26, and continuing on to column 7. The aluminum compound of the '208 patent may be selected in an embodiment as a charge enhancing additive for the colored toner and developer, that is developer without black pigment, of the present invention.
Other representative patents of interest with respect to formation of two-color images include U.S. Pat. Nos. 4,045,218 and 4,572,651, the disclosures of which are totally incorporated herein by reference.
The process of charging a photoresponsive imaging member to a single polarity and creating on it an image consisting of at least three different levels of potential of the same polarity is described in U.S. Pat. No. 4,078,929, the disclosure of which is totally incorporated herein by reference. This patent discloses a method of creating two-colored images by creating on an imaging surface a charge pattern including an area of first charge as a background area, a second area of greater voltage than the first area, and a third area of lesser voltage than the first area with the second and third areas functioning as image areas. The charge pattern is developed in a first step with positively charged toner particles of a first color and, in a subsequent development step, developed with negatively charged toner particles of a second color. Alternatively, charge patterns may be developed with a dry developer containing toners of two different colors in a single development step. Also of interest with respect to the trilevel process for generating images is U.S. Pat. No. 4,686,163, the disclosure of which is totally incorporated herein by reference.
Illustrated in U.S. Pat. No. 4,948,686, the disclosure of which is totally incorporated herein by reference, is a process for forming two-color images which comprises, for example, (1) charging an imaging member in an imaging apparatus; (2) creating on the member a latent image comprising areas of high, intermediate, and low potential; (3) developing the low areas of potential by conductive magnetic brush development with a developer comprising a colored first toner comprising a first resin present in an amount of from about 80 to about 98.8 percent by weight and selected from the group consisting of polyesters, styrene-butadiene polymers, styrene-acrylate polymers, styrene-methacrylate polymers, and mixtures thereof; a first pigment present in an amount of from about 1 to about 15 percent by weight and selected from the group consisting of copper phthalocyanine pigments, quinacridone pigments, azo pigments, rhodamine pigments, and mixtures thereof; a charge control agent present in an amount of from about 0.2 to about 5 percent by weight; colloidal silica surface external additives present in an amount of from about 0.1 to about 2 percent by weight; and external additives comprising metal salts or metal salts of fatty acids present in an amount of from about 0.1 to about 2 percent by weight; and a first carrier comprising a steel core with an average diameter of from about 25 to about 215 microns and a coating selected from the group consisting of methyl terpolymer, polymethyl methacrylate, and a blend of from about 35 to about 65 percent by weight of polymethyl methacrylate and from about 35 to about 65 percent by weight of chlorotrifluoroethylene-vinyl chloride copolymer, wherein the coating contains from 0 to about 40 percent by weight of the coating of conductive particles and wherein the coating weight is from about 0.2 to about 3 percent by weight of the carrier; (4) subsequently developing the high areas of potential by conductive magnetic brush development with a developer comprising a black second toner comprising a second resin present in an amount of from about 80 to about 98.8 percent by weight and selected from the group consisting of polyesters, styrene-butadiene polymers, styrene-acrylate polymers, styrene-methacrylate polymers, and mixtures thereof; a second pigment present in an amount of from about 1 to about 15 percent by weight; and a second charge control additive present in an amount of from about 0.1 to about 6 percent by weight; and a second carrier comprising a steel core with an average diameter of from about 25 to about 215 microns and a coating selected from the group consisting of chlorotrifluoroethylene-vinyl chloride copolymer containing from 0 to about 40 percent by weight of conductive particles at a coating weight of from about 0.4 to about 1.5 percent by weight of the carrier; polyvinylfluoride at a coating weight of from about 0.01 to about 0.2 percent by weight of the carrier; and polyvinylchloride at a coating weight of from about 0.01 to about 0.2 percent by weight of the carrier; and (5) transferring the developed two-color image to a substrate. Imaging members suitable for use with the process of the copending application may be of any type capable of maintaining three distinct levels of potential. Generally, various dielectric or photoconductive insulating material suitable for use in xerographic, ionographic, or other electrophotographic processes may be selected for the above process, and suitable photoreceptor materials include amorphous silicon, layered organic materials as disclosed in U.S. Pat. No. 4,265,990, the disclosure of which is totally incorporated herein by reference, and the like.
The photoresponsive imaging member can be negatively charged, positively charged, or both, and the latent image formed on the surface may be comprised of either a positive or a negative potential, or both. In one embodiment, of the copending application and the present invention the image comprises three distinct levels of potential, all being of the same polarity. The levels of potential should be well differentiated, such that they are separated by at least 100 volts, and preferably 200 volts or more. For example, a latent image on an imaging member can comprise areas of potential at -800, -400, and -100 volts. In addition, the levels of potential may comprise ranges of potential. For example, a latent image may consist of a high level of potential ranging from about -500 to about -800 volts, an intermediate level of potential of about -400 volts, and a low level ranging from about -100 to about -300 volts. An image having levels of potential that range over a broad area may be created such that gray areas of one color are developed in the high range and gray areas of another color are developed in the low range, with 100 volts of potential separating the high and low ranges and constituting the intermediate, undeveloped range. In this situation, from 0 to about 100 volts may separate the high level of potential from the intermediate level of potential, and from 0 to about 100 volts may separate the intermediate level of potential from the low level of potential. When a layered organic photoreceptor is employed, preferred potential ranges are from about -700 to about -850 volts for the high level of potential, from about -350 to about -450 volts for the intermediate level of potential, and from about -100 to about -180 volts for the low level of potential. These potentials can vary depending, for example, upon the type of imaging member selected, and the like.
Moreover, illustrated in copending application U.S. Ser. No. 500,335, the disclosure of which is totally incorporated herein by reference, are developers, toners and imaging processes thereof. In an embodiment of the copending application, there is provided a process for forming two-color images which comprises (1) charging an imaging member in an imaging apparatus; (2) creating on the member a latent image comprising areas of high, intermediate, and low potential; (3) developing the low areas of potential by, for example, conductive magnetic brush development with a developer comprising carrier particles, and a colored first toner comprised of resin particles, colored, other than black, pigment particles, and an aluminum complex charge enhancing additive; (4) subsequently developing the high areas of potential by conductive magnetic brush development with a developer comprising a second black developer comprised of carrier particles and a toner comprised of resin, black pigment, such as carbon black, and a charge enhancing additive; (5) transferring the developed two-color image to a suitable substrate; and (6) fixing the image thereto. In an embodiment of the aforementioned copending application, the first developer comprises, for example, a first toner comprised of resin present in an effective amount of from, for example, about 70 to about 98 percent by weight, which resin can be selected from the group consisting of polyesters, styrene-butadiene polymers, styrene-acrylate polymers, styrene-methacrylate polymers, Pliolites, crosslinked styrene acrylates, crosslinked styrene methacrylates, and the like, wherein the crosslinking component is, for example, divinyl benzene, and mixtures thereof; a first colored blue, especially PV Fast Blue pigment present in an effective amount of from, for example, about 1 to about 15 percent by weight, and preferably from about 1 to about 3 weight percent; an aluminum complex charge enhancing additive; and a second developer comprised of a second toner comprised of resin present in an effective amount of from, for example, about 70 to about 98 percent by weight, which resin can be selected from the group consisting of polyesters, styrene-butadiene polymers, styrene-acrylate polymers, styrene-methacrylate polymers, Pliolites, crosslinked styrene acrylates, crosslinked styrene methacrylates, and the like, wherein the crosslinking component is, for example, divinyl benzene, and mixtures thereof; and a black pigment present in an effective amount of from, for example, about 1 to about 15 percent by weight, and preferably from about 1 to about 5 weight percent wherein the aforementioned black toner contains a charge enhancing additive such as an alkyl pyridinium halide, and preferably cetyl pyridinium chloride, and in a preferred embodiment the black toner is comprised of 92 percent by weight of a styrene n-butyl methyacrylate copolymer (58/42), 6 percent by weight of Regal 330.RTM. carbon black, and 2 percent by weight of the charge enhancing additive cetyl pyridinium chloride.
Although the known processes for forming color images, especially two-color images, are suitable for their intended purposes, a need continues to exist for toners and processes for obtaining color images, and discharge area development processes. In addition, a need exists for a negatively charged toner for use in color imaging processes which toner contains a mixture of components that enable stable triboelectric properties, and rapid desirable charging or admix properties with no, or minimal interaction with the second negatively charged developer used to obtain the two color image. Additionally, there is a need for a two-color image formation process wherein the developers can be of a certain triboelectric charge of, for example, from about 15 to about 35 microcoulombs per gram as determined by known methods, such as the Faraday Cage process, excellent charge distribution and conductivity, and exhibit acceptable admix times of, for example, from about 15 seconds to about 1 minute in embodiments of the present invention. Further, there is a need for a two-color image formation process wherein the toners exhibit similar rheological properties, thereby enhancing fusing, and similar cleaning latitudes, thereby enhancing cleaning of the photoreceptor.